1. Field of the Invention
The invention relates to a strip coating device for continuous coating of strips, particularly metal strips, having at least one application head for applying liquid coating substances to a strip passing through the coating device. The application head has at least one application roller that applies the coating substance to the strip, and at least one supporting roller disposed on the side of the strip opposite the application head.
Within the scope of the invention, strips particularly means metal strips, for example steel strips or aluminum strips. Coating of such strips particularly means application of non-metallic, organic layers or coverings. In this regard, the application of liquid coating substances, for example varnishes or also plastics, is particularly involved. In addition to the application roller, the application head generally has at least one accommodation roller that accommodates the coating substance and gives it off to the application roller, directly or indirectly. If supply of the coating substance takes place by dipping the accommodation roller into a container, this roller is referred to as a scooping roller. If the application head merely consists of the accommodation roller and the application roller, one speaks of a two-roller head, and the accommodation roller then forms a metering roller, at the same time. However, within the scope of the invention, application head also means a so-called three-roller head, in which a metering roller or regulating roller is disposed between the accommodation roller and the application roller. Both two-roller heads and three-roller heads can be equipped to operate by rolling in the same direction or opposite directions.
2. The Prior Art
Strip coating devices are known in which the application head is disposed directly opposite the supporting roller, so that coating essentially takes place against the supporting roller. This has the advantage that the strip is perfectly supported during the coating process. However, in particular when coating thin strips, there is the problem that the coating substance is applied not only onto the strip to be coated, but also directly onto the supporting roller, since the application roller of the application head is generally wider than the strip to be coated, in order to assure a perfect coating process. Such contamination of the supporting roller, which is also called a “tambour,” is particularly undesirable if the position of the strip on the supporting roller changes as the strip passes through. Then an undesirable coating of the back of the strip can occur. The same thing applies in the case that varnish or the like runs onto the supporting roller.
It is therefore also known to provide the supporting roller with a mantle or stocking of rubber, for example, which has a width that is equal to the width of the strip to be coated. A disadvantage of this is the fact that the mantle must be replaced when the strip width changes, so the system must be stopped during the replacement.
Strip coating devices without a supporting roller are known, in which the application head works on a free strip region. The strip to be coated stands under strip tension in this region. It must always be noted that there are geometrical constraints for the strip guidance, because of the ovens that regularly follow the coating devices.